map_index_template does not change the map index displayed in the UI

[TJaniF]

Apache Airflow version

3.0.0

If "Other Airflow 2 version" selected, which one?

main branch

What happened?

In Airflow 2.10.5 the dag below changes the map index displayed in the UI:

from airflow.decorators import dag, task

@dag()
def my_dag():

    @task
    def upstream_task():
        return [1, 2, 3]

    @task(
        map_index_template="Hello! {{ my_custom_template }}",
    )
    def map_me(x, **context):
        print(x)

        from airflow.operators.python import get_current_context

        context = get_current_context()

        context["my_custom_template"] = f"{x}"

    map_me.expand(x=upstream_task())

my_dag()

In RC 2 map_index_template does not change the index. (no errors)

from airflow.decorators import dag, task


@dag
def dtm():

    @task
    def upstream_task():
        return [1, 2, 3]

    @task(
        map_index_template="Hello! {{ my_custom_template }}",
    )
    def map_me(x):
        print(x)

        from airflow.sdk.definitions.context import get_current_context

        context = get_current_context()

        context["my_custom_template"] = f"{x}"

    map_me.expand(x=upstream_task())


dtm()

What you think should happen instead?

No response

How to reproduce

Use the second dag above and run it. See the integer index in the UI.

Operating System

MacOS

Versions of Apache Airflow Providers

Breeze

Deployment

Other

Deployment details

breeze

Anything else?

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[purnachandergit]

Hi, If possible can you assign this to me
I will work on this

thanks

[tirkarthi]

It seems that rendered_map_index is empty in the db and hence map_index is being returned the same in the UI as per #46918 . I couldn't find the implementation that updates this in task-sdk. cc: @kaxil @ashb @amoghrajesh

airflow/airflow-core/src/airflow/models/taskinstance.py

Lines 2765 to 2783 in 23965c4

	def _render_map_index(context: Context, *, jinja_env: jinja2.Environment | None) -> str | None:
	"""Render named map index if the DAG author defined map_index_template at the task level."""
	if jinja_env is None or (template := context.get("map_index_template")) is None:
	return None
	rendered_map_index = jinja_env.from_string(template).render(context)
	log.debug("Map index rendered as %s", rendered_map_index)
	return rendered_map_index
	# Execute the task.
	with set_current_context(context):
	try:
	result = self._execute_task(context, task_orig)
	except Exception:
	# If the task failed, swallow rendering error so it doesn't mask the main error.
	with contextlib.suppress(jinja2.TemplateSyntaxError, jinja2.UndefinedError):
	self._rendered_map_index = _render_map_index(context, jinja_env=jinja_env)
	raise
	else: # If the task succeeded, render normally to let rendering error bubble up.
	self._rendered_map_index = _render_map_index(context, jinja_env=jinja_env)

[tirkarthi]

As per my understanding this needs to be implemented in task-sdk by rendering the values after execution, updating the client and generated datamodels to pass the values similar to how outlet_events is passed currently. The API server has to update the values for the taskinstance in db as the client posts them while marking the ti state. Given the requirement to improve RC2 stability and the changes involved this feels like a candidate for 3.1+.

[TJaniF]

As per my understanding this needs to be implemented in task-sdk by rendering the values after execution, updating the client and generated datamodels to pass the values similar to how outlet_events is passed currently. The API server has to update the values for the taskinstance in db as the client posts them while marking the ti state. Given the requirement to improve RC2 stability and the changes involved this feels like a candidate for 3.1+.

Yeah, that sounds like a bigger lift. Thank you for investigating! :)